It is well known to coat the back of tufted carpets with adhesive materials to anchor component fibers in a desired configuration. The adhesive coating anchors the individual pile yarns to the carpet backing and prevents unwanted fiber movement and slippage which might otherwise result in fuzzing or wrinkling of the carpet. Excess adhesive, however, can intrude through the carpet backing to the face of the carpet, thereby causing undue stiffness in the pile yarns. Accordingly, it is important that penetration of adhesive into the backs of the pile yarns and into the carpet backing be carefully controlled so that adequate fiber anchoring is achieved without intrusion of adhesive into the face or pile surface of the carpet.
The amount of adhesive used and uniformity of application affect the flexibility or hand of the carpet. Additionally, it is important to control the amount of adhesive applied for economic reasons. Thus, a method of coating is needed which achieves a uniform coating and minimum waste while minimizing the amount of adhesive employed.
Carpet coating materials have been previously applied using several different methods. One such method comprises using a spray system with single or multiple spray nozzles mounted in fixed or traversable carriages to spray the back of the carpet with an adhesive material. Coating uniformity and weight are difficult to control because of the overlap of spray patterns and the variation of spray output caused by nozzle blockage. Additionally, overspray of the edges of the carpet usually occurs, resulting in wasted adhesive.
Another method of coating the back of a carpet is a transfer coating method. A layer of coating material is formed on a moving surface such as a roll, and the back of the carpet is pressed on wiped against the preformed layer to transfer the coating material from the moving surface to the carpet back. Adequate control of the amount of coating material transferred to the carpet is difficult to achieve because the layer of coating material on the roll cannot be transferred uniformly to the rough surface which is characteristic of a carpet back. Also, because of the inherently large contact area between the roll and the carpet back, the force exerted by the roll against the carpet is spread out over such a large area that there is insufficient pressure between them, making adequate penetration of the coating material into the pile yarn backs hard to achieve.
The most widely used carpet coating method comprises applying an excess of adhesive directly onto the carpet back, and then scraping the deposited adhesive with a bar or blade to spread the adhesive and remove the excess. Using this method, however, it is extremely difficult to control the amount of adhesive used and the degree of penetration achieved. Factors such as the viscosity fo the coating material, the absorbency of the carpet fibers, the amount of excess coating material deposited on the carpet back, the dwell time between deposition and scraping of the coating material, and the ambient conditions all affect the amount of coating material used and the degree of penetration achieved.